Bicycles conventionally utilize a chain drive to transmit power from the pedal actuated drive sprocket to a smaller driven sprocket fixedly attached to the hub of the rear wheel. Speed changing devices may be employed and these generally include, in a ten speed bicycle, a second drive sprocket having fewer sprocket teeth than the first drive sprocket, a multi-unit driven sprocket having five different size sprocket wheels connected to the hub of the rear wheel, and chain shifting mechanism that enables the drive chain to be shifted from one drive sprocket to the other and from one driven sprocket to another, thus giving ten speed combinations for a constant pedal rotation rate.
Bicycles employing hydraulic drive mechanisms have been proposed in the past, as in U.S. Pat. Nos. 485,094, 3,811,704, 3,850,448, and 4,078,816 and Belgian Pat. No. 537,981. In general, however, the mechanisms disclosed provided for a single speed transmission, or, as in U.S. Pat. No. 485,094, a single speed transmission capable of providing an incremental higher speed. None of the disclosures make any reference to the fact that it is often necessary to remove the hydraulically driven wheel for repair or other servicing, and hence no mechanism was disclosed that would facilitate removal of the wheel. More importantly, there is no disclosure that would permit removal of the wheel while preserving the integrity of the hydraulic circuit to the drive wheel motor.